Ink jet recording systems are classified mainly into a system in which droplets are ejected (or expelled) by applying pressure through piezoelectricity-to-mechanical conversion, a system in which bubbles are produced through electricity-to-heat conversion, thereby ejecting droplets under pressure, and a system in which droplets are ejected with suction by an electrostatic force.
Requirements for ink jet inks include, for example, adaptation to the recording system chosen from the foregoing, high recording image density and superior image color, superior color image fastness, rapid fixability onto a recording medium without bleeding of the image, superior storage stability and low cost.
In light of the foregoing, there have been studied and proposed various ink jet recording liquids but ones which simultaneously satisfy many requirements are limited.
Conventional dyes and pigments having known Color Index (C.I.) nimbers described in the C.I. have been studied for use in color image recording with yellow, magenta, cyan and black. Water-soluble dyes including, for example, a xanthene type such as C.I. Acid Red 52 and an azo type such as C.I. Direct Red 20 are known among magenta inks. Whereas these inks have high reliability with respect to not clogging in printers, there are problems in fastness such as light-fastness and water resistance. Inks using quinacridone type pigments such as C.I. Pigment Red 122 are known, which exhibit high fastness but tends to cause problems such as insufficient print density and bronzing. In commonly known conventional dyes and pigments, t is difficult that image color and fastness required for an ink for ink jet recording are compatible with each other.
Recently, in view of the foregoing, there have been proposed various dyes and pigments for use in ink jet recording. Specifically in magenta dyes, an improvement in light-fastness is desired and, for example, an ink containing a water-soluble pyrazole azo dye, for example, was disclosed in JP-A No. 2002-226752 (hereinafter, the term JP-A refers to unexamined Japanese Patent Application Publication). Further, anthrapyridine compounds and a water-based ink composition using the same were disclosed in JP-A Nos. 10-306221, 2000-169776 and 2001-72884. In the art of rapid progress, how ever, their levels are insufficient and desired were further improvements in water resistance and light-fastness.
Occlusion of a dye in dispersed polyurethane or polyester particles was proposed to improve water resistance and light-fastness, as described in JP-A Nos.58-45272, 6-340835, 7-268257 and 7-268260. These techniques achieved improved water resistance and light-fastness but its level was still insufficient, furthermore, producing problems that color tone was not necessarily sufficient and dispersion stability was insufficient when occluded at a relatively high concentration.